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How Your Body Handles Cholesterol

How does cholesterol contribute to the threat of heart disease, strokes, and certain types of cancer? The answer is quite remarkable. One of your liver's primary objectives is to
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transport the saturated fat you have eaten to other tissues of the body. This task is not an easy one because fats can't dissolve in your bloodstream. (You know the saying, "Oil and Water don't mix".) The liver must therefore repackage the fat with other more dissolvable substances before it can travel through your bloodstream: it builds, in effect, a miniature "shuttle bus". The outer frame of the shuttle bus is made up of protein and the inside is filled with saturated fat and cholesterol. 

Once the bus is full, it is sealed and shipped out of the liver to enter the bloodstream. The outer protein shell of the bus allows part of the fat and cholesterol to dissolve and float freely. As the shuttle bus passes by muscles, it opens its doors and allows some fat to be taken up. As a rule, when your muscles are not working vigorously, they prefer to burn fat, thus preserving their stores of carbohydrates for use as high-octane fuel during strenuous exercise. (Your heart muscle in particular likes to burn fat for energy.) The shuttle bus eventually transports any additional saturated fat throughout your bloodstream to be stored in your fat cells. This is how your fat cells become enlarged and you begin to look fat. 

But what about the cholesterol in the shuttle bus? It is also delivered to your body cells. In the adrenal glands, cholesterol is used to make hormones such as cortisone. In the ovaries, it is used to make estrogen and progesterone. In the male testes, it is the building block of the male hormone testosterone. Cholesterol is also used to build bile acids, vitamin D, and part of the fatty, waxy membrane around the outside of every body cell. 

So far so good – your body needs a certain amount of cholesterol to remain healthy. However, when you consume a diet high in saturated fat and/or cholesterol, the shuttle busses transport more cholesterol than your body cells require for their normal functions. In this situation, the shuttle bus doors can open and allow excess cholesterol to exit into the bloodstream, where it becomes stuck to the inside linings of the blood vessel walls. This process causes the blood vessels to narrow, eventually restricting the circulation of blood. 

This narrowing process, known as atherosclerosis (hardening of the arteries), is the major contributing cause of heart disease, stroke, and related cardiovascular diseases. Less blood and oxygen can circulate to the heart muscle, resulting in an angina episode or a heart attack. In the brain, these narrowed vessels become rigid, losing their elasticity. Then they are more easily ruptured, resulting in a stroke. 

The Big Plaque Attack 

The cholesterol that gets laid down in your arteries from the cholesterol shuttle bus forms the main component of arterial plaque. As the arterial plaque thickens over your lifetime, your heart arteries (coronary arteries) and other arteries become narrower. Once an artery is almost completely obstructed by arterial plaque, you become a prime candidate for a heart attack, stroke, or even kidney failure. Unfortunately, arterial narrowing due to arterial plaque is completely invisible and painless until the final stages. That is why death by heart attack or stroke can happen suddenly with no warning signs. 

It is, of course, human nature not to pay attention to things that we can't see or feel. The Dental Association has a relatively easy job convincing us to floss and brush our teeth to prevent the build-up of dental plaque. We can feel plaque on our teeth, but what about plaque in our arteries? We can't see or feel that. 

Yet no one has ever died because of dental plaque on their teeth. Arterial plaque, on the other hand, is life threatening. Fifty percent of North Americans die of cardiovascular diseases, most of them as a result of obstructed and rigid arteries. Just because you can't see it or feel it doesn't mean you should ignore it. If you are lucky, you will get advance warning of the build-up of arterial plaque – the squeezing chest and arm pain of angina. Unfortunately, for 25 percent of the people with advanced blood vessel narrowing, sudden death by heart attack is their first and last symptom of heart disease. 

To make matters worse, some evidence suggests that excess cholesterol delivered to your fat tissues, adrenal glands, ovaries, and testes may over stimulate the production of certain hormones and produce abnormally formed hormones. Imbalances in these reproductive hormones have been associated with the increased risk of breast cancer, prostate cancer, and other cancers of the reproductive organs. 

In a nutshell, eating foods high in saturated fat forces the liver to manufacture large quantities of cholesterol. Any excess cholesterol travelling through the bloodstream sticks to the inside walls of your arteries. Cumulative lifetime narrowing of the arteries is one of the main reasons why you can feel fine one minute and die of a heart attack the next. It's the old story of the straw that broke the camel's back: every mouthful of saturated fat that you eat adds another layer of arterial plaque. One day the artery may be completely obstructed. How long do you plan to wait before you appreciate the full impact that high-fat foods have on your life expectancy? 

References:

Nutrition recommendations. The report of the scientific review committee, 1990. Minister of National Health and Welfare Canada. pp. 43, 45. 

Behme M. Symposium on Diet, Nutrition and health. Nutrition Today, 1977; 32:23-29. 

Karmali, R. Fatty acids: inhibition, 1987. American Journal of Clinical Nutrition;

45:225-9. 

Dwyer J. T. Health aspects of vegetarian diets. American Journal of Clinical Nutrition, 1988; 48:712-38. 

Castelli W. P. et al. Cutting back on saturated fat and cholesterol, 1988. Post Grad Medical Journal; 82:44-56.

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